It wasn't just any cop. Stephanie Lazarus was a well respected, highly decorated female detective with the Los Angeles Police Department. And it wasn't just a minor crime. She was charged with the murder of Sherri Rasmussen, a young nurse, 23 years after the killing.

"A Los Angeles police officer arrested for murder is just - it's a bombshell! I mean, you just don't get those kinda cases!" says Andrew Blankstein. "People were really stunned by this."

Blankstein and Joel Rubin cover the police beat for the Los Angeles Times and are consultants to "48 Hours."

"Nobody saw this coming. Nobody says she was a cop that they saw on the edge," Rubin says. "As far as we can tell, people in the department saw her as, you know, a cop's cop, a good cop."

"She's been a longtime patrol detective," Blankstein adds. "She was with the art theft detail in commercial crimes… which is theft of high-end art in L.A .And in doing those kind of investigations… it gets a lot of press, a lot of attention… If the police and prosecutors are going to be believed, she's harboring a secret about murder for 23 years!"

At first glance, Stephanie Lazarus has no obvious connection to the victim in this murder case - Sherri Rasmussen, a highly regarded nursing administrator.

Sherri came from a very close-knit family. Her parents, Nels and Loretta Rasmussen, adored their three daughters and their growing family.

"…Sherri was the glue that held the family together all the time…..and made everything that much better," says Sherri's younger sister, Teresa, tells "48 Hours Mystery" correspondent Maureen Maher.

But in February 1986, Sherri would be attacked, beaten and shot to death in her Los Angeles home.

"We were an ordinary family, you know... You never think something like this is gonna happen to you," says Teresa. She says she never could have anticipated that only just now - more than 20 years after her sister's murder - there's been arrest.

"It doesn't make the pain any less," she says. "You start the grieving process all over again, one more time."

The pain is most obvious when the family visits Sherri's grave.

"I don't believe that you can understand the grief… a part of your life has just been taken away forever," Nels Rasmussen tells Maher in an exclusive interview.

Her parents say Sherri excelled at everything she did. She became a nurse when she was only 20. At age 27, she was named director of critical care nursing at Glendale Adventist Medical Center, where she sometimes lectured.

"She liked taking care of people and making sure things were done right, that people were cared for properly," says Loretta Rasmussen.

"She said, 'I'm gonna elevate the stature of nursing in the nation,'" Nels recalls. "And she was on her way."

On top of a successful career, in early 1986, Sherri was extraordinarily happy, having just married the man she loved. Her new husband was John Ruetten, a young engineer she'd met in 1984.

As it would turn out, John was the single link to the woman accused of murdering his new bride.

That is because Stephanie Lazarus was Ruetten's ex-girlfriend. And according to Sherri's friends and family, Stephanie was not willing to give up the man she'd first met in college several years before the murder.

"Sherri was competition," Teresa says. "If she could get Sherri outta the way, then possibly John would be free to be with her again."

John is the one who discovered his wife's body.

"He was in a daze," Teresa explains. "He was sort of the deer in the headlights look, you know?"

John Ruetten has had little to say publicly since his wife's murder in 1986.

He briefly addressed mourners at a hospital memorial service for Sherri, telling them, "I just want to thank you all for coming and I want you to know that Sherri was the best professional in the world - she was the best wife that anybody could ever have."

"To me, he's kind of a central character that we really know the least about," says Blankstein.

"There's a lot of questions left unanswered," adds Rubin.

Questions like: what did John Ruetten know? Or suspect? He says that early on, he told detectives to talk to his ex-girlfriend - an L.A.P.D. cop.

"John is really the only person that has this connection to both women that can tell us what was going on to some extent?" Maher asks Rubin. "You would think, yeah," he replies.

But police were off chasing other leads, and Sherri's friend, Jayne Goldberg, says that Ruetten just quietly faded out of sight, leaving her quite angry.

"I would have expected that John would have been much more involved in the investigation… and demand answers," she says.

Especially, as months - and then years - went by with no resolution to the case.

"He should have been her advocate. She would have been his," Goldberg says. "Why wasn't he camped outside the police station? I don't understand it!"